mathtool2/lib/tools/chi_square.dart

// tools/chi_square.dart
import 'package:fl_chart/fl_chart.dart';
import 'package:flutter/material.dart';

import 'tool_kit.dart';

/// 卡方检验（2×2 列联表）。
///
///     K² = n(ad − bc)² / ((a+b)(c+d)(a+c)(b+d))，n = a+b+c+d
///
/// 精确值给分数、近似值给小数，都从 Symja 拿。图表里的比例数据同样走 Symja
/// （`N[...]`），Dart 只负责把数字喂给 fl_chart —— 图表不参与复制。
class ChiSquarePage extends StatefulWidget {
  const ChiSquarePage({super.key});

  @override
  State<ChiSquarePage> createState() => _ChiSquarePageState();
}

class _ChiSquarePageState extends State<ChiSquarePage> {
  // 2×2 列联表就照列联表的样子排：a b 一行、c d 一行
  final _a = ToolField('a', hint: '第一行左');
  final _b = ToolField('b', hint: '第一行右', rowWithPrevious: true);
  final _c = ToolField('c', hint: '第二行左');
  final _d = ToolField('d', hint: '第二行右', rowWithPrevious: true);

  @override
  Widget build(BuildContext context) => ToolScaffold(
    title: '卡方检验',
    fields: [_a, _b, _c, _d],
    intro: const Text('请输入 2×2 列联表数据:'),
    compute: (session) async {
      final a = _need(_a);
      final b = _need(_b);
      final c = _need(_c);
      final d = _need(_d);
      final bind = 'a=$a,b=$b,c=$c,d=$d';

      final k2 =
          'With[{$bind}, Module[{nn=a+b+c+d}, '
          'nn*(a*d-b*c)^2/((a+b)*(c+d)*(a+c)*(b+d))]]';

      // 各组比例（给图表，不复制）：组1 = a/(a+b)、b/(a+b)，组2 = c/(c+d)、d/(c+d)
      final prop = 'With[{$bind}, N[{a/(a+b), b/(a+b), c/(c+d), d/(c+d)}]]';
      final p = parseSymjaList((await session.compute(prop)).text);
      final n0 = p.isNotEmpty ? asNumber(p[0]) ?? 0.0 : 0.0;
      final n1 = p.length > 1 ? asNumber(p[1]) ?? 0.0 : 0.0;
      final n2 = p.length > 2 ? asNumber(p[2]) ?? 0.0 : 0.0;
      final n3 = p.length > 3 ? asNumber(p[3]) ?? 0.0 : 0.0;

      return [
        ...await exactAndApprox(session, 'K²', k2),
        ToolChart('各组比例', _barChart(n0, n1, n2, n3)),
      ];
    },
  );

  /// 等高堆积条形图：两组各按 类别A / 类别B 的比例堆积，纵轴百分比。
  Widget _barChart(double a1, double b1, double a2, double b2) => Column(
    mainAxisSize: MainAxisSize.min,
    children: [
      SizedBox(
        height: 220,
        child: BarChart(
          BarChartData(
            alignment: BarChartAlignment.spaceAround,
            maxY: 1.0,
            barTouchData: BarTouchData(enabled: false),
            titlesData: FlTitlesData(
              show: true,
              bottomTitles: AxisTitles(
                sideTitles: SideTitles(
                  showTitles: true,
                  getTitlesWidget: (value, meta) =>
                      Text(value.toInt() == 0 ? '组1' : '组2'),
                ),
              ),
              leftTitles: AxisTitles(
                sideTitles: SideTitles(
                  showTitles: true,
                  reservedSize: 40,
                  getTitlesWidget: (value, meta) =>
                      Text('${(value * 100).toInt()}%'),
                ),
              ),
              topTitles: AxisTitles(sideTitles: SideTitles(showTitles: false)),
              rightTitles: AxisTitles(
                sideTitles: SideTitles(showTitles: false),
              ),
            ),
            gridData: FlGridData(
              show: true,
              drawVerticalLine: false,
              getDrawingHorizontalLine: (value) => FlLine(
                color: Colors.grey.withValues(alpha: 0.3),
                strokeWidth: 1,
              ),
            ),
            borderData: FlBorderData(show: false),
            barGroups: [
              BarChartGroupData(
                x: 0,
                groupVertically: true,
                barsSpace: 4,
                barRods: [
                  BarChartRodData(
                    fromY: 0,
                    toY: a1,
                    color: Colors.blue,
                    width: 30,
                  ),
                  BarChartRodData(
                    fromY: a1,
                    toY: a1 + b1,
                    color: Colors.red,
                    width: 30,
                  ),
                ],
              ),
              BarChartGroupData(
                x: 1,
                groupVertically: true,
                barsSpace: 4,
                barRods: [
                  BarChartRodData(
                    fromY: 0,
                    toY: a2,
                    color: Colors.blue,
                    width: 30,
                  ),
                  BarChartRodData(
                    fromY: a2,
                    toY: a2 + b2,
                    color: Colors.red,
                    width: 30,
                  ),
                ],
              ),
            ],
          ),
        ),
      ),
      const SizedBox(height: 10),
      Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          _legend(Colors.blue, '类别A'),
          const SizedBox(width: 20),
          _legend(Colors.red, '类别B'),
        ],
      ),
    ],
  );

  Widget _legend(Color color, String text) => Row(
    mainAxisSize: MainAxisSize.min,
    children: [
      Container(width: 16, height: 16, color: color),
      const SizedBox(width: 8),
      Text(text),
    ],
  );

  /// 取一个标量输入框：空着或填了多个值都直接报中文错。
  String _need(ToolField f) {
    if (f.count == 0) throw Exception('请填写「${f.label}」');
    if (f.count > 1) throw Exception('「${f.label}」只能填一个数');
    return f.text;
  }
}